iOS v13.5.1 Https requests errors /CORS and preflight error

We have noticed that https requests on iOS v13.5.1 are failing. Some are facing preflight errors or typical CORS errors.
Requests working perfectly fine for Android app and Browsers. It’s happening only on ios.
our iOS version is 13.5.1

Ionic:

ionic (Ionic CLI) : 4.10.3 (/usr/local/lib/node_modules/ionic)
Ionic Framework : @ionic/angular 5.0.7
@angular-devkit/build-angular : 0.803.26
@angular-devkit/schematics : 8.3.26
@angular/cli : 8.3.26
@ionic/angular-toolkit : 2.2.0

Cordova:

cordova (Cordova CLI) : 8.1.2 (cordova-lib@8.1.1)
Cordova Platforms : android 8.1.0, browser 6.0.0, ios 5.0.0
Cordova Plugins : cordova-plugin-ionic-keyboard 2.2.0, cordova-plugin-ionic-webview 5.0.0, (and 7 other plugins)

System:

ios-sim : 7.0.0
NodeJS : v10.16.2 (/usr/local/bin/node)
npm : 6.9.0
OS : macOS High Sierra
Xcode : Xcode 10.1 Build version 10B61

NOTE:Even if I set res.setHeader('Access-Control-Allow-Origin', '*'); on the backend side,it won’t work

We have this doc for just this reason.

CORS related issues could be a few things, so please review and double check your setup.